YouTube is basically my TV lol
Hopefully my answers help you with your project!
1) To be honest I watch a bit of everything, from gamers to beauty girls. I'm subscribed to a bit more than 60 channels and most of them are comedy related. I also watch a lot of food related channels and people who live in japan.
2) I watch fail army, nigahiga, shane dawson, good mythical morning, simon&martina, rachel&jun, texan in tokyo, cooking with dog, pewdiepie, cutiepiemarzia, swoozie, matt stonie, mytoecold, kinoshita yuka, maangchi, miles jai, domics, casey naistat, will akana, cyanide & happiness and a lot of ASMR channels. Why? Mainly entertainment and the japanese channels for knowledge too. Some channels that I follow I just keep watching since I've been subscribed for too long and nostalgia makes me keep watching even though I don't enjoy the content as much as before (hence pewdiepie and nigahiga, had the same problem with smosh but they changed their videos way too much so I was able to unsubscribe lol)
3) As soon as I realize there's some clickbait element into it, I stop watching (like "Why I stopped doing x thing" and the video is 9 minutes long and they only start talking about the title at 7m mark and so on). Also audio is a huge deal for me since I use headphones and I'm sensitive to that (example: there's a great channel of a sushi chef but the audio of his videos is crap since he records from his restaurant and I can't watch his videos due the crappy audio). Also if the person is too cheesy I stop the video, like when they are trying too hard to add jokes or make angles effects (like jumping from side to side of the screen and so on).
4) Is very hard to come up with an unique channel, most topics have been covered but what I enjoy is when someone has an unique style to add into the mix, like a format or something personal that makes your channel different and makes you come back for more. For example look at mytoecold and Will Akana, same type of channels (one to one stand up comedy kinda thing) but completely different between each other. That's what I enjoy of YouTube and that's what makes me stay and watch (: